1. Field of the Invention
The present invention relates generally to a method and apparatus for directly sintering metal powder, and more particularly to a method and apparatus for directly sintering metal powder on a work-space platform under a high temperature environment in a layer by layer manner. The present invention relates to a method and apparatus that is capable of producing composite parts with two types of material.
2. Description of the Background Art
Various methods have been proposed in the background art for forming three-dimensional objects by deposition of layers of material on a substrate. This layered manufacturing process is also known as solid free-form fabrication (SFF) or rapid prototyping (RP). Various materials and combinations of materials can be processed according to this method, including materials such as plastics, waxes, metals, ceramics, and the like. U.S. Pat. No. 5,252,264 to Foderhase et al. describes an example of this type of method and apparatus for producing prototype parts. Foderhase et al. describe a method and apparatus for producing prototype parts with multiple powder pistons by fusing selected portions of a layer of powder at a target area.
The RP technology has been successfully used to provide all kinds of prototypes, such as visual, functional, and production prototypes. However, RP techniques have limited impact if used solely for direct fabrication of prototypes. The advantages of RP, such as flexibility in free-form fabrication without geometric constraints, fast material processing time, and innovative joining techniques, have great potential in reducing time to fabricate a complex tooling. In the fiercely competitive market, RP techniques are applied on rapid tooling (RT) to shorten the lead-time of tooling preparation and to further reduce the time-to-market of a new product.
RT technology is typically categorized as either indirect rapid tooling or direct rapid tooling. Indirect rapid tooling processes start with a pattern made by the RP process, and a tooling is duplicated with the pattern by casting or spraying, etc. In direct tooling processes, a tooling is fabricated by the RP machine through sintering, bonding, curing, depositing, etc. without any intermediate steps. Among the metal powder forming processes, selective laser sintering (SLS), direct metal laser sintering (DMLS), and laser generating (LG) or laser engineered net shaping (LENS) are well known.
The SLS process has been developed by DTM Corporation of Austin. The system includes a 50W, CO2 laser unit, a feed-powder cartridge, a laser scanning unit, a build-cylinder, and a powder feeder. In operation, a motor drives the powder feeder to a specified amount at which a volume of powder extends above a leveling plane. The feed-powder cartridge travels across the leveling plane and delivers the powder to the target area. In the target area, a laser beam is generated by laser apparatus and is deflected by galvanometer-controlled mirrors. The rotation of the mirror is controlled by a computer corresponding to the cross-section of the layer of the part to be produced. When a layer of the part is produced, the powder will be selectively fused. Once a layer is finished, the process is repeated until the part is built up, layer by layer.
U.S. Pat. No. 4,863,538 issued on Sep. 5, 1989 to Deckard; U.S. Pat. No. 4,938,816 issued on Jul. 3, 1990 to Beaman et al.; U.S. Pat. No. 4,944,817 issued on Jul. 31, 1990 to Bourell et al.; PCT publication WO 88/02677 published on Apr. 21, 1998; U.S. Pat. No. 5,147,587 issued on Sep. 15, 1992 to Marcus et al.; U.S. Pat. No. 5,156,697 issued on Oct. 20, 1992 to Bourell et al.; and U.S. Pat. No. 5,182,170 issued on Jan. 26, 1993 to Marcus et al. all describe detailed, exemplary method and apparatus of the process described hereinabove; the entirety of each of which is herein incorporated by reference.
Several kinds of material with powder form, such as polymer, nylon and metal, are often used in the SLS system. The tooling materials available are Copper Polyamide and Rapid Steel. Rapid Steel 2.0 is a polymer-coated stainless steel powder. It can be used to create tooling for the bridge or pre-production injection molding. A binder melted during laser sintering holds the stainless steel powder together. In a Rapid Steel process, only polymer-binder is melted. The metal does not melt by the laser during the sintering because the laser energy, e.g., 50W, is not high enough to heat the powder up to the melting point of the metal.
After all layers are scanned, the insert is prepared for the first furnace cycle, as the mold insert created is now a green part. During the first furnace cycle, the binder decomposes and the steel powder sinters to form small necks (or bridges) between particles. The resulting part, which is 60% dense, is called a xe2x80x9cbrownxe2x80x9d insert and is much more durable than the green insert. The brown part is placed in a crucible and a measured amount of bronze is placed next to the part. The crucible is then placed in the furnace for the second furnace cycle. The bronze melts and wicks into the brown part by capillary action, forming the infiltrated part. The resulting mold inserts are therefore fully dense. However, the post-process procedure is extremely time consuming and involves considerable effort.
In mid-1998, DTM introduced Copper Polyamide (PA), a heat resistant, thermally conductive composite of copper and plastic that can be used to create tooling for short runs of production equivalent plastic parts. In operation, the metal powder of copper does not melt. Instead, the plastic composite fuses to bond the powder together.
DMLS is another metal laser forming process developed by Electro Optics Systems (EOS) of Munich in Germany. Commercialized machine, EOSINT M machine, has been developed and commercialized since 1995. The machine consists of a 200 W, CO2 laser unit, a laser scanning unit, a building platform, and a scraper assembly. The building process is similar to an SLS process. An exemplary method and apparatus are further described in U.S. Pat. No. 6,042,774, issued in Mar. 28, 2000 to Wilkening et al, the entirety of which is herein incorporated by reference.
A metal powder often used in EOSINT is a mixture of bronze, nickel, and copper-phosphide. In this powder, copper-phosphide melts at 660xc2x0 C. and acts as the low temperature-binding agent. When the laser beam exposes on the powder, bronze and nickel powders homogenize at high temperature. Copper-phosphide powder melts, and the liquid phase penetrates the surrounding cavities, wets the bronze/nickel particles and bonds the particles together. After sintering, the part density is about 70% of the theoretical density of the material.
Based on the well-known laser cladding process (Hoadley and Drezet, 1991), the laser generating (LG) method was developed at the Technische Hochschule in Aachen as xe2x80x9claser-aided powder solidificationxe2x80x9d (LAPS) (Kreutz et al., 1995), in the Los Alamos National Laboratory as xe2x80x9cdirected light fabricationxe2x80x9d (DLF) (Lewis, 1995), and at Sandia Laboratories as xe2x80x9claser engineered net shapingxe2x80x9d (LENS). In LENS at Sandia Laboratories, the system uses a robotically controlled laser to melt metal powder to create custom parts in a special chamber. The chamber is purged with argon, which acts as a protective atmosphere for the powder metals during the melting process.
Operating inside the chamber is a six-axis robot programmed to go through the motions necessary to build a particular part. The powder metal is fed through a cable to the articulated arm of the robot. Simultaneously, a laser beam travels through a fiber optic cable to deliver energy. LG is the only RT technique able to directly produce filly dense parts (N. P. Karapatis et al. 1998).
However, the required laser power and beam quality are usually high, e.g. the laser power is normally higher than 1 kW. In addition, the process itself induces high thermal stresses that can lead to part failure. Geometric accuracy and part stability are difficult to generate because of the lack of supporting material. Geometry of the parts is often limited to rather simple shapes. Due to applying high power and laser quality, as well as complicated mechanical structure for powder and laser delivery, the LENS system is more expensive than an SLS system (R. Irving, 1999).
All of these systems are demonstrative of attempts to generate three-dimensional objects using metal powder through laser sintering. However, numerous problems, such as low density of the part fabricated in SLS and EOS system, distortion, geometric limitation and the high costs of the LENS system, have limited the practical application of these systems.
The aforementioned discussion of the background art included several references to a variety of references acknowledged only by their author(s) and publication date. The following bibliographic description of these references is provided hereinafter, the entirety of each of which is herein incorporated by reference. Hoadley, A. and Drezet, J. M. (1991), xe2x80x9cModelisation thermique de la refusion et du traitement de surface par laser, Lasers de puissance et traitement des materiaux,xe2x80x9d Ecole de Printemps, Sireuil, France, May 28-31, 1991; Kreutz, E. W., Backes, G., Gasser, A. and Wissebach, K., xe2x80x9cRapid prototyping With CO2 laser radiationxe2x80x9d, Applied Surface Science, Vol.86 No.1, (1995), pp 310-316; Lewis, G. K., xe2x80x9cDirect laser metal deposition process fabricates near-net-shape components rapidly,xe2x80x9d Materials Technology, Vol. 10, (1995), pp3-4; N. P. Karapatis et al., xe2x80x9cDirect rapid tooling: a review of current research,xe2x80x9d Rapid Prototyping Journal, Vol. 4,No. 2, (1998), pp 77-89; and Robert Irving, xe2x80x9cTaking a powder,xe2x80x9d Mechanical Engineering, Sep. 1999, pp55-59.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
An object of the present invention is to improve production efficiency and product density during the production of three dimensional, layered products.
An object of the present invention is to provide controlled, reliable part production of components from more than one material and within a high production temperature environment.
These and other objects are accomplished by a method for producing a desired, three dimensional metallic part, comprising the steps of heating a part production apparatus to a setting temperature; maintaining the setting temperature during a fabrication period; depositing a powder onto a target surface, the powder comprising first and second materials; accurately controlling a layer thickness; preventing the powder from leaking from a primary powder container under a high temperature environment; and sintering a selected portion of the powder corresponding to a relative cross-sectional region of the desired part.
These and other objects are further accomplished by a sintering apparatus for producing a three dimensional metallic part from at least one metallic powder, the sintering apparatus comprising a laser for selectively melting the at least one metallic powder; a scanner head mounted along a laser beam travel path, the scanner head focusing and directing a laser beam; a working chamber for high temperature sintering of the at least one metallic powder; an airtight chamber for maintaining an inert gas seal, the airtight chamber enclosing the working chamber; a secondary powder container; a scraper for delivering the at least one metallic powder to a target area; a heating system for heating the apparatus to a setting temperature; a cylinder and piston assembly for dispensing and building the at least one metallic powder to form the metallic part; and means for controlling the sintering apparatus.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.